Clinical evidence suggests that hearing loss during infancy and childhood increases the probability of language and learning disabilities. Experimental data suggest that such communicative disorders are due in part to changes in auditory system anatomy and function, induced by lack of acoustic experience during development. These considerations indicate the importance of understanding auditory development, and the degree to which experience can influence its course. Developmental studies can also provide insight into the function of the adult auditory system. The proposed research will investigate several current problems in normal auditory development, including: the afferent and efferent innervation of the organ of Corti; cochlear blood flow and its relationship to cochlear metabolism; ion distribution in stria vascularis and the ionic composition of endolymph; neural function in the dorsal cochlear nucleus; the growth of neurons and synapses in the cochlear nuclear complex. In addition, the neural plasticity of auditory development will be studied in a series of experiments. The effects of profound acoustic deprivation during auditory development upon the function of the auditory system will be studied. Acoustic deprivation will include surgical removal of the middle ear transmission apparatus to provide approximately 60 dB of isolation from air-conducted, and 40 dB of isolation from bone-conducted stimuli. A sound-attenuated rearing environment will provide an additional 80 dB of isolation from external sounds. Mechanical displacement of the tapes with a piezoelectric driver is used to restore auditory function. In addition, animals will be reared in an environment restricted to a 1/3 octave band of noise and assessed in adulthood with the 2-deoxyglucose technique to determine whether experience produces preferential representation in the central auditory pathway. Also, mid-cochlear lesions will be created mechanically to produce a gap in the central auditory place map, at different developmental ages. The 2-deoxyglucose technique will be used to determine whether function is restored to these regions. If so HRP labeling of primary afferents will be used to study the source of re-innervating fibers, and single unit studies will explore the function of the re-innervated neurons. Finally, the effects of neonatal lesions of the cochlear efferents will be assessed both anatomically and functionally.